Sony removed The Sims 3 from the PlayStation Store years ago. You cannot buy it digitally for Vita/PSP legally anymore. Your only legal digital option is buying a or PSP Go that already has the game installed via an old PSN account (which is a gray area).
Some users turn to torrent sites to download .iso files. However, this method comes with significant risks, including exposure to malware and legal repercussions. Free Download Psp Games The Sims 3.iso
This is the definitive experience. You can buy The Sims 3 + all expansions for cheap during Steam sales. While it isn't the PSP story, you get open worlds, Create-a-Style, and seasons. Sony removed The Sims 3 from the PlayStation Store years ago
Consider The Sims 4, The Sims FreePlay, or other life simulation games available on various platforms. Some users turn to torrent sites to download
The PPSSPP Emulator is free and open-source software that allows you to run PSP games in higher resolutions than the original hardware.
The Sims 3 was released for various platforms, including PC, Mac, Xbox 360, PlayStation 3, and Wii. However, there isn't an official PSP version of the game available as an ISO file or any other format.